Swift 语言基础(4)-控制流

for 循环

for ... in ... 循环

 forindexin 1...5{
  println("\(index)times 5 is \(index* 5)")
 }
 // 1 times 5 is 5
 // 2 times 5 is 10
 // 3 times 5 is 15
 // 4 times 5 is 20
 // 5 times 5 is 25

 letbase= 3
 letpower= 10
 varanswer= 1
 for _ in1...power{
 answer*=base
 }
 println("\(base)to the power of \(power)is\(answer)")
 // prints "3 to the power of 10 is 59049"

 letnames= ["Anna","Alex","Brian","Jack"]
 fornamein names {
println("Hello,\(name)!")
 }
 // Hello, Anna!
 // Hello, Alex!
 // Hello, Brian!
 // Hello, Jack!

 letnumberOfLegs= ["spider":8,"ant":6,"cat":4]
 for(animalName,legCount)innumberOfLegs {
     println("\(animalName)s have \(legCount)legs")
 }
 // spiders have 8 legs
 // ants have 6 legs
// cats have 4 legs

 forcharacterin "Hello" {
println(character)
 }
 // H
 // e
 // l
 // l
 // o

For-Condition-Increment

 for varindex= 0;index< 3; ++index{
println("index is\(index)")
 }
 // index is 0
 // index is 1
 // index is 2

 varindex:Int
 forindex= 0;index< 3; ++index{
println("index is\(index)")
 }
// index is 0
 // index is 1
 // index is 2
 println("The loop statements were executed\(index)times")
 // prints "The loop statements were executed 3 times"

while 循环

 varsquare= 0
 vardiceRoll= 0
 whilesquare< finalSquare {
// roll the dice
if++diceRoll==7 { diceRoll = 1 }
// move by the rolled amount
square+=diceRoll
ifsquare< board.count{
// if we're still on the board, move up or down for a snake or a ladder
square+=board[square]
}
  }

println("Game over!")

 do{
// move up or down for a snake or ladder
square+=board[square]
// roll the dice
if++diceRoll==7 { diceRoll = 1 }
 // move by the rolled amount
square+=diceRoll
 }while square < finalSquare
 println("Game over!")

条件语句

if

var temperatureInFahrenheit = 30
 iftemperatureInFahrenheit<= 32 {
println("It's very cold. Consider wearing a scarf.")
 }
 // prints "It's very cold. Consider wearing a scarf."

 temperatureInFahrenheit=40
 if temperatureInFahrenheit<= 32 {
println("It's very cold. Consider wearing a scarf.")
 }else{
println("It's not that cold. Wear a t-shirt.")
 }
 // prints "It's not that cold. Wear a t-shirt."

 temperatureInFahrenheit=90
 if temperatureInFahrenheit<= 32 {
println("It's very cold. Consider wearing a scarf.")
 }else if temperatureInFahrenheit >= 86 {
println("It's really warm. Don't forget to wear sunscreen.")
 }else{
println("It's not that cold. Wear a t-shirt.")
 }
 // prints "It's really warm. Don't forget to wear sunscreen."

temperatureInFahrenheit = 72
 if temperatureInFahrenheit <= 32 {
 println("It's very cold. Consider wearing a scarf.")
 } else if temperatureInFahrenheit >= 86 {
 println("It's really warm. Don't forget to wear sunscreen.")
 }

switch

 let someCharacter: Character = "e"
 switch someCharacter {
 case "a", "e", "i", "o", "u":
 println("\(someCharacter) is a vowel")
 case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m",
 "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
 println("\(someCharacter) is a consonant")
 default:
 println("\(someCharacter) is not a vowel or a consonant")
} //
prints "e is a vowel"

没有隐性陷入

 let anotherCharacter: Character = "a"
 switch anotherCharacter {
 case "a":
 case "A":
 println("The letter A")
 default:
 println("Not the letter A")
 }
 // this will report a compile-time error

范围匹配

 let count = 3_000_000_000_000
 let countedThings = "stars in the Milky Way"
 var naturalCount: String
 switch count {
 case 0:
naturalCount = "no"
 case 1...3:
naturalCount = "a few"
 case 4...9:
naturalCount = "several"

case 10...99:
naturalCount = "tens of"
case 100...999:
naturalCount = "hundreds of"
case 1000...999_999:
naturalCount = "thousands of"
default:
naturalCount = "millions and millions of"
} 

println("There are \(naturalCount) \(countedThings).")
// prints "There are millions and millions of stars in the Milky Way."

元组匹配

 let somePoint = (1, 1)
 switch somePoint {
 case (0, 0):
println("(0, 0) is at the origin")
 case (_, 0):
println("(\(somePoint.0), 0) is on the x-axis")
 case (0, _):
println("(0, \(somePoint.1)) is on the y-axis")
 case (-2...2, -2...2):
println("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
println("(\(somePoint.0), \(somePoint.1)) is outside of the box")
} //
prints "(1, 1) is inside the box"

值绑定

 let anotherPoint = (2, 0)
 switch anotherPoint {
 case (let x, 0):
println("on the x-axis with an x value of \(x)")
case (0, let y):
 println("on the y-axis with a y value of \(y)")
 case let (x, y):
  println("somewhere else at (\(x), \(y))")
 }
// prints "on the x-axis with an x value of 2"

附加条件

 let yetAnotherPoint = (1, -1)
 switch yetAnotherPoint {
 case let (x, y) where x == y:
 println("(\(x), \(y)) is on the line x == y")
 case let (x, y) where x == -y:
  println("(\(x), \(y)) is on the line x == -y")
 case let (x, y):
  println("(\(x), \(y)) is just some arbitrary point")
 }
// prints "(1, -1) is on the line x == -y"

控制流变换语句

continue

 let puzzleInput = "great minds think alike"
var puzzleOutput = ""
 for character in puzzleInput {
 switch character {
 case "a", "e", "i", "o", "u", " ":
 continue
 default:
 puzzleOutput += character
 }

break

 let numberSymbol: Character = "三" // Simplified Chinese for the number 3
 var possibleIntegerValue: Int?
 switch numberSymbol {
 case "1", "١", "一", "๑":
 possibleIntegerValue = 1
 case "2", "٢", "二", "๒":
  possibleIntegerValue = 2
 case "3", "٣", "三", "๓":
  possibleIntegerValue = 3
case "4", "٤", "四", "๔":
possibleIntegerValue = 4
default:
break
} 

if let integerValue = possibleIntegerValue {
println("The integer value of \(numberSymbol) is \(integerValue).")
} else {
println("An integer value could not be found for \(numberSymbol).")
} //
prints "The integer value of 三 is 3."

fallthrough

 let integerToDescribe = 5
 var description = "The number \(integerToDescribe) is"
switch integerToDescribe {
 case 2, 3, 5, 7, 11, 13, 17, 19:
 description += " a prime number, and also"
 fallthrough
 default:
  description += " an integer."
 }
println(description)
// prints "The number 5 is a prime number, and also an integer."

标签语句

gameLoop: while square != finalSquare {
if ++diceRoll == 7 { diceRoll = 1 }
switch square + diceRoll {
case finalSquare:
// diceRoll will move us to the final square, so the game is over
break gameLoop
case let newSquare where newSquare > finalSquare:
// diceRoll will move us beyond the final square, so roll again
continue gameLoop
default:
// this is a valid move, so find out its effect
square += diceRoll
square += board[square]
}
} 

println("Game over!")